Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$109.42	8.179%	$118.3695	$118.37	$118.35	$118.40
Purchase #2	$161.40	7.115%	$172.8836	$172.88	$172.90	$172.90
Purchase #3	$26.33	11.155%	$29.2671	$29.27	$29.25	$29.30
Purchase #4	$141.28	3.143%	$145.7204	$145.72	$145.70	$145.70
Purchase #5	$26.28	4.467%	$27.4539	$27.45	$27.45	$27.50
Purchase #6	$130.78	7.176%	$140.1648	$140.16	$140.15	$140.20
Purchase #7	$32.88	12.217%	$36.8969	$36.90	$36.90	$36.90
7 purchase totals =	$628.37		$670.7562	$670.75	$670.70	$670.90